1. Field of the Invention
This invention relates to a wet process for removing hydrogen sulfide from a hydrogen sulfide-containing gas by absorption and recovering the removed hydrogen sulfide in the form of elementary sulfur, and more particularly to a process for recovering sulfur from hydrogen sulfide-containing gases by washing a hydrogen sulfide-containing gas such as coke oven gases, coal gases, flue gases from oil refineries, natural gas, flue gases from rayon plants, exhaust gases from sewage disposal plants, exhaust gases from geothermal power plants, and other similar gases containing small amounts of hydrogen sulfide, with an alkaline aqueous solution to effect absorption of hydrogen sulfide by the aqueous solution and contacting the absorbed hydrogen sulfide with molecular oxygen in the presence of a catalyst contained in the aqueous solution to separate out elementary sulfur.
Stating more particularly, this invention relates to an improvement in a process for the recovery, in the form of elementary sulfur, of hydrogen sulfide by in the aforementioned hydrogen sulfide-containing gases, which improvement resides in using, as a catalyst, a composition comprising an organic redox catalyst such as a naphthoquinone sulfonate, a polyvalent metal compound and a water-soluble high molecular compound having a weight-average molecular weight of from 300 to 50,000.
2. Description of Prior Art
Heretofore, the wet process for desulfurization of hydrogen sulfide-containing gases by the use of a catalyst comprising a naphthoquinone sulfonate has been well known as Takahax Process. One of the present inventors has suggested in U.S. Pat. No. 4,002,727 that a catalyst composition comprising a naphthoquinone sulfonate and a polyvalent metal compound, when added in a small amount to an absorbent used for the desulfurization, suppresses otherwise possible secondary production of a thiosulfate and permits recovery of sulfur to be effected in high yields.
It has been found, however, that even by the process disclosed in U.S. Pat. No. 4,002,727, the polyvalent metal compound is liable, in the course of the desulfurization and depending on the operating conditions, to form sulfides, hydroxides or oxides partially and deposit such products within the desulfurization system and that the deposits shorten the period in which the catalyst manifests high activity and, consequently, lower the ratio of sulfur recovery and suffer impurities to mingle into the recovered sulfur to an extent of degrading the hue and purity of sulfur. Further in accordance with this process, in a large scale desulfurization plant, the sulfur separated in the process, the polyvalent metal compound incorporated in the catalyst, the heavy metal compound naturally brought into the system, and the organic and inorganic impurities present in the gases under treatment are cumulatively deposited on the packing material filling the absorption tower or in the circulatory absorption line laid in the bottom of the tower, frequently to clog the system. Once the system is clogged, the operation of the plant must be stopped and the system cleaned.
An object of this invention, therefore, is to provide a novel process for the desulfurization of hydrogen sulfide-containing gases.
Another object of this invention is to provide a process for recovering elementary sulfur of high purity by subjecting hydrogen sulfide-containing gases to wet desulfurization.
Yet another object of this invention is to provide a process for the desulfurization of hydrogen sulfide-containing gases, which process precludes deposition of polyvalent metal compounds in the system and permits the operation thereof to proceed without interruption for a long time.